Wavelength division multiplexing/demultiplexing devices employing patterned optical components

ABSTRACT

Improved wavelength division multiplexing/demultiplexing devices are disclosed. In the case of an improved wavelength division multiplexing device having a diffraction grating for combining a plurality of monochromatic optical beams into a multiplexed, polychromatic optical beam, the improvement comprises employing a plurality of patterned optical input components corresponding to the plurality of monochromatic optical beams, wherein each of the plurality of patterned optical input components introduces a first patterned phase delay into a corresponding one of the plurality of monochromatic optical. beams. The improvement also comprises employing a patterned optical output component for introducing a second patterned phase delay into the multiplexed, polychromatic optical beam, wherein the first patterned phase delay and the second patterned phase delay are added so as to reshape the passband of the improved wavelength division multiplexing device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is related to U.S. Pat. No. 5,999,672, issuedDec. 7, 1999; U.S. Pat. No. 6,011,884, issued Jan. 4, 2000; U.S. patentapplication Ser. No. 09/257,045, filed Feb. 25, 1999;, now U.S. Pat. No.6,137,433, U.S. patent application Ser. No. 09/323,094, filed Jun. 1,1999;, now U.S. Pat. No. 6,263,135, U.S. patent application Ser. No.09/342,142, filed Jun. 29, 1999; now U.S. Pat. No. 6,289,155, U.S.patent application Ser. No. 09/382,492, filed Aug. 25, 1999, pending,;U.S. patent application Ser. No. 09/382,624, filed Aug. 25, 1999; nowU.S. Pat. No. 6,271,970, U.S. patent application Ser. No. 09/363,041,filed Jul. 29, 1999; U.S. patent application Ser. No. 09/363,042, filedJul. 29, 1999; now U.S. Pat. No. 6,236,780, U.S. patent application Ser.No. 09/392,670, filed Sep. 8, 1999;, now U.S. Pat. No. 6,298,182, andU.S. patent application Ser. No. 09/392,831, filed Sep. 8, 1999; nowU.S. Pat. No. 6,181,853, all of which are hereby incorporated byreference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to wavelength divisionmultiplexing and, more particularly, to wavelength divisionmultiplexing/demultiplexing devices employing patterned opticalcomponents.

BACKGROUND OF THE INVENTION

Optical communication technology relies on wavelength divisionmultiplexing (WDM) to provide increased bandwidth over existinginstalled fiber, as well as newly deployed fiber installations. Severaltechnologies exist to provide the technical solution to WDM: arraywaveguide gratings (AWG's), fiber Bragg grating based systems,interference filter based systems, Mach-Zehnder interferometric basedsystems, and diffraction grating based systems, to name a few. Eachsystem has advantages and disadvantages over the others.

Diffraction grating based systems have the advantage of parallelism,which yields higher performance and lower cost for high channel countsystems. One drawback to traditional diffraction grating based systems,however, is an insertion loss that rises quickly and monotonically asthe source illumination drifts off of the center of the desiredcommunication channel wavelength. That is, traditional diffractiongrating based systems invariably suffer from a variation in transmissionefficiency across a wavelength channel. This variation in transmissionefficiency with wavelength creates deleterious effects on modulatedsignals. For analog signals it creates harmonic distortion, for digitalsignals it increases the bit-error-rates at higher modulationbandwidths.

Also, most traditional diffraction grating based systems have aninherently gaussian-shaped passband profile. Such a gaussian-shapedpassband profile is generally very narrow with a single peak and steeppassband edges. Thus, even when a communication channel drifts off ofits center wavelength by only a slight amount, signal coupling with areceiving fiber is often severely detrimentally affected.

At least one attempt has been made to alleviate at least one aspect ofthe above-described shortcomings. For example, as described by D. Wiselyin “High Performance 32 Channel HDWDM Multiplexer with 1 nm ChannelSpacing and 0.7 nm Bandwidth”, SPIE, Vol. 1578, Fiber Networks forTelephony and CATV (1991), a microlens may be employed at the end of aninput fiber in a WDM device so as to widen the gaussian-shaped passbandprofile of the WDM device. That is, by widening the gaussian-shapedpassband profile of the WDM device, there is less susceptibility towavelength drift in communication channels. However, widening thegaussian-shaped passband profile of a WDM device may increase thechances of channel crosstalk. Thus, a tradeoff determination must bemade when deciding whether or not to implement the above-describedtechnique.

While no other known attempts have been made to alleviate one or moreaspects of the above-described shortcomings, it is presumed that suchother attempts, if made, would also require certain tradeoffs to bemade. Thus, in view of the foregoing, it would be desirable to provide aWDM device which overcomes the above-described inadequacies andshortcomings with minimal or no tradeoffs in an efficient and costeffective manner.

OBJECTS OF THE INVENTION

The primary object of the present invention is to provide wavelengthdivision multiplexing/demultiplexing devices which overcome theabove-described inadequacies and shortcomings with minimal or notradeoffs in an efficient and cost effective manner.

The above-stated primary object, as well as other objects, features, andadvantages, of the present invention will become readily apparent tothose of ordinary skill in the art from the following summary anddetailed descriptions, as well as the appended drawings. While thepresent invention is described below with reference to preferredembodiment(s), it should be understood that the present invention is notlimited thereto. Those of ordinary skill in the art having access to theteachings herein will recognize additional implementations,modifications, and embodiments, as well as other fields of use, whichare within the scope of the present invention as disclosed and claimedherein, and with respect to which the present invention could be ofsignificant utility.

SUMMARY OF THE INVENTION

According to the present invention, improved wavelength divisionmultiplexing/demultiplexing devices are provided. In the case of animproved wavelength division multiplexing device having a diffractiongrating for combining a plurality of monochromatic optical beams into amultiplexed, polychromatic optical beam, the improvement comprisesemploying a plurality of patterned optical input componentscorresponding to the plurality of monochromatic optical beams, whereineach of the plurality of patterned optical input components introduces afirst patterned phase delay into a corresponding one of the plurality ofmonochromatic optical beams. The improvement also comprises employing apatterned optical output component for introducing a second patternedphase delay into the multiplexed, polychromatic optical beam, whereinthe first patterned phase delay and the second patterned phase delay areadded so as to reshape the passband of the improved wavelength divisionmultiplexing device.

In accordance with other aspects of the present invention, the pluralityof patterned optical input components comprises a plurality of patternedphase masks, wherein each of the plurality of patterned phase masksintroduce the first patterned phase delay into a corresponding one ofthe plurality of monochromatic optical beams. Each of the plurality ofpatterned phase masks is preferably formed on/in a correspondingcollimating microlens. Alternatively, the plurality of patterned opticalinput components also comprises a plurality of collimating microlenses,wherein each of the plurality of collimating microlenses collimates acorresponding one of the plurality of monochromatic optical beams. Ineither case, each corresponding collimating microlens or each of theplurality of collimating microlenses contributes to a widening of thepassband of the improved wavelength division multiplexing device.

In accordance with further aspects of the present invention, each of theplurality of patterned phase masks has a periodic phase profile. Abenefit to this aspect is that the passband of the improved wavelengthdivision multiplexing device is typically a gaussian-shaped passbandhaving a peak, and the periodic phase profile of each patterned phasemask contributes to a flattening of the peak of the gaussian-shapedpassband of the improved wavelength division multiplexing device.Another benefit to this aspect is that the passband of the improvedwavelength division multiplexing device is a gaussian-shaped passbandhaving sideband slopes, and the periodic phase profile of each patternedphase mask contributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisionmultiplexing device.

In accordance with still further aspects of the present invention, eachof the plurality of patterned phase masks has a non-periodic phaseprofile. A benefit to this aspect is that the passband of the improvedwavelength division multiplexing device is a gaussian-shaped passbandhaving a peak, and the non-periodic phase profile of each patternedphase mask contributes to a flattening of the peak of thegaussian-shaped passband of the improved wavelength divisionmultiplexing device. Another benefit to this aspect is that the passbandof the improved wavelength division multiplexing device is agaussian-shaped passband having sideband slopes, and the non-periodicphase profile of each patterned phase mask contributes to a steepeningof the sideband slopes of the gaussian-shaped passband of the improvedwavelength division multiplexing device.

In accordance with other aspects of the present invention, the patternedoptical output component comprises a patterned phase mask forintroducing the second patterned phase delay into the multiplexed,polychromatic optical beam. The patterned phase mask is preferablyformed on/in a focusing microlens. Alternatively, the patterned opticaloutput component also comprises a focusing microlens for focusing themultiplexed, polychromatic optical beam. In either case, the focusingmicrolens contributes to a widening of the passband of the improvedwavelength division multiplexing device.

In accordance with further aspects of the present invention, thepatterned phase mask has a periodic phase profile. A benefit to thisaspect is that the passband of the improved wavelength divisionmultiplexing device is a gaussian-shaped passband having a peak, and theperiodic phase profile of the patterned phase mask contributes to aflattening of the peak of the gaussian-shaped passband of the improvedwavelength division multiplexing device. Another benefit to this aspectis that the passband of the improved wavelength division multiplexingdevice is a gaussian-shaped passband having sideband slopes, and theperiodic phase profile of the patterned phase mask contributes to asteepening of the sideband slopes of the gaussian-shaped passband of theimproved wavelength division multiplexing device.

In accordance with still further aspects of the present invention, thepatterned phase mask has a non-periodic phase profile. A benefit to thisaspect is that the passband of the improved wavelength divisionmultiplexing device is a gaussian-shaped passband having a peak, and thenon-periodic phase profile of the patterned phase mask contributes to aflattening of the peak of the gaussian-shaped passband of the improvedwavelength division multiplexing device. Another benefit to this aspectis that the passband of the improved wavelength division multiplexingdevice is a gaussian-shaped passband having sideband slopes, and thenon-periodic phase profile of the patterned phase mask contributes to asteepening of the sideband slopes of the gaussian-shaped passband of theimproved wavelength division multiplexing device.

In accordance with other aspects of the present invention, the pluralityof patterned optical input components and the patterned optical outputcomponent cause either constructive or destructive interference to occuras wavelength varies over the passband of the improved wavelengthdivision multiplexing device when the first patterned phase delay andthe second patterned phase delay are added. Also, the plurality ofmonochromatic optical beams and the multiplexed, polychromatic opticalbeam are beneficially arranged in input and output arrays, respectively,wherein each of the plurality of patterned optical input components andthe patterned optical output component has a patterned phase mask, andwherein each patterned phase mask is oriented at an angle relative tothe input and output arrays. Further, at least the plurality ofpatterned optical input components or the patterned optical outputcomponent are beneficially formed adjacent to a plurality ofnon-patterned optical input components or a non-patterned optical outputcomponent, respectively.

In the case of an improved wavelength division demultiplexing devicehaving a diffraction grating for separating a multiplexed, polychromaticoptical beam into a plurality of monochromatic optical beams, theimprovement comprises employing a patterned optical input component forintroducing a first patterned phase delay into the multiplexed,polychromatic optical beam. The improvement also comprises employing aplurality of patterned optical output components corresponding to theplurality of monochromatic optical beams, wherein each of the pluralityof patterned optical output components introduces a second patternedphase delay into a corresponding one of the plurality of monochromaticoptical beams. The first patterned phase delay and the second patternedphase delay are added so as to reshape the passband of the improvedwavelength division demultiplexing device.

In accordance with other aspects of the present invention, the patternedoptical input component comprises a patterned phase mask for introducingthe first patterned phase delay into the multiplexed, polychromaticoptical beam. The patterned phase mask is preferably formed on/in acollimating microlens. Alternatively, the patterned optical outputcomponent further comprises a collimating microlens for collimating themultiplexed, polychromatic optical beam. In either case, the collimatingmicrolens contributes to a widening of the passband of the improvedwavelength division demultiplexing device.

In accordance with further aspects of the present invention, thepatterned phase mask has a periodic phase profile. A benefit to thisaspect is that the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having a peak, andthe periodic phase profile of the patterned phase mask contributes to aflattening of the peak of the gaussian-shaped passband of the improvedwavelength division demultiplexing device. Another benefit to thisaspect is that the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having sidebandslopes, and the periodic phase profile of the patterned phase maskcontributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.

In accordance with still further aspects of the present invention, thepatterned phase mask has a non-periodic phase profile. A benefit to thisaspect is that the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having a peak, andthe non-periodic phase profile of the patterned phase mask contributesto a flattening of the peak of the gaussian-shaped passband of theimproved wavelength division demultiplexing device. Another benefit tothis aspect is that the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having sidebandslopes, and the non-periodic phase profile of the patterned phase maskcontributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.

In accordance with other aspects of the present invention, the pluralityof patterned optical output components comprises a plurality ofpatterned phase masks, wherein each of the plurality of patterned phasemasks introduces the second patterned phase delay into a correspondingone of the plurality of monochromatic optical beams. Each of theplurality of patterned phase masks is preferably formed on/in acorresponding focusing microlens. Alternatively, the plurality ofpatterned optical output components also comprises a plurality offocusing microlenses, wherein each of the plurality of focusingmicrolenses focuses a corresponding one of the plurality ofmonochromatic optical beams. In either case, each corresponding focusingmicrolens or each of the plurality of focusing microlenses contributesto a widening of the passband of the improved wavelength divisiondemultiplexing device.

In accordance with further aspects of the present invention, each of theplurality of patterned phase masks has a periodic phase profile. Abenefit to this aspect is that the passband of the improved wavelengthdivision demultiplexing device is a gaussian-shaped passband having apeak, and the periodic phase profile of each patterned phase maskcontributes to a flattening of the peak of the gaussian-shaped passbandof the improved wavelength division demultiplexing device. Anotherbenefit to this aspect is that the passband of the improved wavelengthdivision demultiplexing device is a gaussian-shaped passband havingsideband slopes, and the periodic phase profile of each patterned phasemask contributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.

In accordance with still further aspects of the present invention, eachof the plurality of patterned phase masks has a non-periodic phaseprofile. A benefit to this aspect is that the passband of the improvedwavelength division demultiplexing device is a gaussian-shaped passbandhaving a peak, and the non-periodic phase profile of each patternedphase mask contributes to a flattening of the peak of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device. Another benefit to this aspect is that thepassband of the improved wavelength division demultiplexing device is agaussian-shaped passband having sideband slopes, and the non-periodicphase profile of each patterned phase mask contributes to a steepeningof the sideband slopes of the gaussian-shaped passband of the improvedwavelength division demultiplexing device.

In accordance with other aspects of the present invention, the patternedoptical input component and the plurality of patterned optical outputcomponents cause either constructive or destructive interference tooccur as wavelength varies over the passband of the improved wavelengthdivision demultiplexing device when the first patterned phase delay andthe second patterned phase delay are added. Also, the multiplexed,polychromatic optical beam and the plurality of monochromatic opticalbeams are beneficially arranged in input and output arrays,respectively, wherein each of the patterned optical input component andthe plurality of patterned optical output components has a patternedphase mask, and wherein each patterned phase mask is oriented at anangle relative to the input and output arrays. Further, at least thepatterned optical input component or the plurality of patterned opticaloutput components are formed adjacent to a non-patterned optical inputcomponent or a plurality of non-patterned optical output components,respectively.

The present invention will now be described in more detail withreference to exemplary embodiments thereof as shown in the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a fuller understanding of the present invention,reference is now made to the appended drawings. These drawings shouldnot be construed as limiting the present invention, but are intended tobe exemplary only.

FIG. 1a is a side view of a preferred embodiment of a wavelengthdivision multiplexing device employing patterned optical components inaccordance with the present invention.

FIG. 1b is a top view of the wavelength division multiplexing deviceshown in FIG. 1a.

FIG. 1c is an end view of the optical fibers and the correspondingpatterned optical components, along section A—A of FIGS. 1a and 1 b.

FIG. 2a is a perspective view of a coupling device containing aplurality of laser diodes for replacing the plurality of optical inputfibers in the multiplexing device shown in FIGS. 1a and 1 b.

FIG. 2b is a perspective view of a coupling device containing aplurality of photodetectors for replacing the plurality of opticalfibers in the demultiplexing device shown in FIGS. 3a and 3 b.

FIG. 3a is a side view of a preferred embodiment of a wavelengthdivision demultiplexing device employing patterned optical components inaccordance with the present invention.

FIG. 3b is a top view of the wavelength division demultiplexing deviceshown in FIG. 3a.

FIG. 4a is side view of a first embodiment of one of the plurality ofpatterned optical input components shown in FIG. 1.

FIG. 4b is a side view of a first embodiment of the patterned opticaloutput component shown in FIGS. 1a and 1 b.

FIG. 5a is a side view of a bi-convex collimating/focusing microlenshaving a pure convex surface on one side and a patterned phase maskconvex surface on the opposite side in accordance with the presentinvention.

FIG. 5b is a side view of a plano-convex collimating/focusing microlenshaving a pure planar surface on one side and a patterned phase maskconvex surface on the opposite side in accordance with the presentinvention.

FIG. 6 is a front view of a substrate having an array of patterned andnon-patterned microlenses formed therein in accordance with the presentinvention.

FIG. 7 is a plot of the gaussian-shaped passband profile of the improvedwavelength division demultiplexing device of FIGS. 3a and 3 b that iswidened as a result of the use of non-phase masked microlenses.

FIG. 8 is a plot of the profile of a cosinusoidal patterned phase maskin accordance with the present invention.

FIG. 9 is a plot of the passband profile of the improved wavelengthdivision demultiplexing device of FIGS. 3a and 3 b that is flattened asa result of the use of cosinusoidal patterned phase mask microlenses inaccordance with the present invention.

FIG. 10a indicates how the periodic wavefront profiles that are formedfrom the cosinusoidal patterned phase mask microlenses described in FIG.8 are constructively added to each other when they are completely inphase on center channel, thereby diffracting the maximum amount ofenergy out of the receiving fiber core, in accordance with the presentinvention.

FIG. 10b indicates how the periodic wavefront profiles that are formedfrom the cosinusoidal patterned phase mask microlenses described in FIG.8 are destructively canceled when they are 180 degrees out of phase offcenter channel in accordance with the present invention.

FIG. 11 shows a plot of the widened gaussian-shaped passband profileshown in FIG. 7 in comparison to a plot of the widened and flattenedpassband profile shown in FIG. 9.

FIG. 12 is a plot of the profile of a chirped patterned phase mask inaccordance with the present invention.

FIG. 13 is a plot of the passband profile of the improved wavelengthdivision demultiplexing device of FIGS. 3a and 3b that is flattened as aresult of the use of chirped patterned phase mask microlenses inaccordance with the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

Referring to FIGS. 1a and 1 b, there are shown a side view and a topview, respectively, of a preferred embodiment of a wavelength divisionmultiplexing device 10 employing patterned optical components inaccordance with the present invention. The multiplexing device 10comprises a plurality of optical input fibers 12, a correspondingplurality of patterned optical input components 14, acollimating/focusing lens 16, a reflective diffraction grating 18, apatterned optical output component 20, and a corresponding opticaloutput fiber 22. All of the above-identified components of themultiplexing device 10 are disposed along an optical axis Z—Z of themultiplexing device 10, as will be described in more detail below.

At this point it should be noted that the optical input fibers 12 andthe optical output fibers 22, as well as any other optical fibersdescribed herein, are single mode optical fibers. Of course, however,this does not limit the present invention to use with only single modeoptical fibers. For example, the present invention can also be used withmultimode optical fibers.

The plurality of optical input fibers 12, as well as the correspondingplurality of patterned optical input components 14, are arranged intoone-dimensional input arrays (e.g., 1×33 arrays). The patterned opticaloutput component 20, as well as the corresponding optical output fiber22, are also arranged into one-dimensional output arrays (i.e., 1×1arrays). For ease of alignment, each of the plurality of patternedoptical input components 14 may be secured to the end of a correspondingone of the plurality of optical input fibers 12, but the presentinvention is not limited in this regard. For example, each of theplurality of patterned optical input components 14 may be aligned with,but separated from, the end of a corresponding one of the plurality ofoptical input fibers 12. Similarly, for ease of alignment, the patternedoptical output component 20 may be secured to the end of thecorresponding optical output fiber 22, but the present invention is notlimited in this regard. For example, the patterned optical outputcomponent 20 may be aligned with, but separated from, the end of thecorresponding optical output fiber 22. For purposes of ease of opticalfiber handling and precision placement, both the plurality of opticalinput fibers 12 and the optical output fiber 22 may be secured within,for example, silicon V-groove assemblies.

Referring to FIG. 1c, there is shown an end view of the plurality ofoptical input fibers 12, as well as the corresponding plurality ofpatterned optical input components 14, along section A—A of FIGS. 1a and1 b. Each of the plurality of optical input fibers 12 is aligned with acorresponding one of the plurality of patterned optical input components14. Both the plurality of optical input fibers 12 and the correspondingplurality of patterned optical input components 14 are arranged as 1×33arrays.

Also referring to FIG. 1c, there is shown an end view of the patternedoptical output component 20, as well as the corresponding optical outputfiber 22, along section A—A of FIG. 1a and 1 b. The patterned opticaloutput component 20 is aligned with the corresponding optical outputfiber 22. Both the patterned optical output component 20 and thecorresponding optical output fiber 22 are arranged as 1×1 arrays.

Returning to FIGS. 1a and 1 b, each of the plurality of optical inputfibers 12 transmits a single, monochromatic optical input beam 24, whilethe optical output fiber 22 receives a single, multiplexed,polychromatic optical output beam 26. Each of the monochromatic opticalinput beams 24 being transmitted from the plurality of optical inputfibers 12 is carrying a single channel of data at a unique wavelength,which is preferably, but not required to be, within the infrared (IR)region of the electromagnetic spectrum. The single channel of data thatis being carried by each monochromatic optical input beam 24 issuperimposed on each corresponding unique wavelength by means (e.g.,laser diodes connected to the plurality of optical input fibers 12),which are not shown here and which do not form a part of this invention,but are well known in the art. The unique wavelengths of themonochromatic optical input beams 24 are appropriately preselected suchthat the data channels generally do not interfere with each other (i.e.,there is sufficient channel spacing), and the optical transmissionlosses through both the optical input fibers 12 and the optical outputfiber 22 are low, as is also well known in the art.

The multiplexed, polychromatic optical output beam 26 being received bythe optical output fiber 22 is carrying a plurality of channels of dataat the unique wavelengths of corresponding ones of the plurality ofmonochromatic optical input beams 24. That is, the multiplexed,polychromatic optical output beam 26 is carrying a plurality of channelsof data (e.g., 33 channels of data) at the unique wavelengths of themonochromatic optical input beams 24 that are transmitted from theoptical input fibers 12. The plurality of monochromatic optical inputbeams 24 are combined into the multiplexed, polychromatic optical outputbeam 26 through the combined operation of the collimating/focusing lens16 and the reflective diffraction grating 18, as will be described inmore detail below.

At this point it should be noted that the plurality of optical inputfibers 12 (as well as the corresponding plurality of patterned opticalinput components 14) and the patterned optical output component 20 (aswell as the corresponding optical output fiber 22) are disposed offsetfrom, but symmetrically about, the optical axis Z—Z of the multiplexingdevice 10 so as to insure that the multiplexed, polychromatic opticaloutput beam 26 is directed to the patterned optical output component 20and the corresponding optical output fiber 22, and not to anywhere else.This offset spacing of the plurality of optical input fibers 12 (as wellas the corresponding plurality of patterned optical input components 14)and the patterned optical output component 20 (as well as thecorresponding optical output fiber 22) is determined based upon thefocusing power of the collimating/focusing lens 16, as well as thecharacteristics of the diffraction grating 18 and the wavelengths ofeach of the monochromatic optical input beams 24.

Each of the plurality of monochromatic optical input beams 24 istransmitted from its corresponding optical input fiber 12 through acorresponding one of the plurality of patterned optical input components14 and into the air space between the plurality of patterned opticalinput components 14 and the collimating/focusing lens 16. Within thisair space, the plurality of monochromatic optical input beams 24 expandin diameter until they become incident upon the collimating/focusinglens 16. The collimating/focusing lens 16 collimates each of theplurality of monochromatic optical input beams 24, and then transmitseach collimated, monochromatic optical input beam 24′ to the reflectivediffraction grating 18.

At this point it should be noted that the optical axis of thecollimating/focusing lens 16 coincides with the optical axis Z—Z of themultiplexing device 10 so as to insure that the multiplexed,polychromatic optical output beam 26 is directed to the patternedoptical output component 20 and the corresponding optical output fiber22, and not to anywhere else, as will be described in more detail below.

The reflective diffraction grating 18 operates to angularly disperse theplurality of collimated, monochromatic optical input beams 24′ by anamount that is dependent upon the wavelength of each of the plurality ofcollimated, monochromatic optical input beams 24′. Also, the reflectivediffraction grating 18 is oriented at a special angle (i.e., the Littrowdiffraction angle, α_(i)) relative to the optical axis Z—Z of themultiplexing device 10 in order to obtain the Littrow diffractioncondition for an optical beam having a wavelength that lies within ornear the wavelength range of the plurality of collimated, monochromaticoptical input beams 24′. The Littrow diffraction condition requires thatan optical beam be incident on and reflected back from a reflectivediffraction grating at the exact same angle. Therefore, it will bereadily apparent to one skilled in the art that the reflectivediffraction grating 18 is used to obtain near-Littrow diffraction foreach of the plurality of collimated, monochromatic optical input beams24′.

The Littrow diffraction angle, α_(i), is determined by the well-knowndiffraction grating equation,

mλ=2 d(sin α_(i))

wherein m is the diffraction order, λ is the wavelength, d is thediffraction grating groove spacing, and α_(i) is the common angle ofincidence and reflection. It will be readily apparent to one skilled inthe art that the Littrow diffraction angle, α_(i), depends upon numerousvariables, which may be varied as necessary to optimize the performanceof the multiplexing device 10. For example, variables affecting theLittrow diffraction angle, α_(i), include the desired gratingdiffraction order, the grating line pitch, and the wavelength range ofthe multiplexing device 10, among others.

At this point it should be noted that the reflective diffraction grating18 can be formed from a variety of materials and by a variety oftechniques. For example, the reflective diffraction grating 18 can beformed by a three-dimensional hologram in a polymer medium, or byreplicating a mechanically ruled master with a polymer material. In bothcases, the polymer is preferably overcoated with a thin, highlyreflective metal layer such as, for example, gold or aluminum.Alternatively, the reflective diffraction grating 18 can be formed bychemically etching into a planar material such as, for example, glass orsilicon, which is also preferably overcoated with a thin, highlyreflective metal layer such as, for example, gold or aluminum.

As previously mentioned, the reflective diffraction grating 18 operatesto angularly disperse the plurality of collimated, monochromatic opticalinput beams 24′. Thus, the reflective diffraction grating 18 removes theangular separation of the plurality of collimated, monochromatic opticalinput beams 24′, and reflects a collimated, polychromatic optical outputbeam 26′ back towards the collimating/focusing lens 16. The collimated,polychromatic optical output beam 26′ contains each of the uniquewavelengths of the plurality of collimated, monochromatic optical inputbeams 24′. Thus, the collimated, polychromatic optical output beam 26′is a collimated, multiplexed, polychromatic optical output beam 26′. Thecollimating/focusing lens 16 focuses the collimated, multiplexed,polychromatic optical output beam 26′. The resulting multiplexed,polychromatic optical output beam 26 is transmitted from thecollimating/focusing lens 16 through the patterned optical outputcomponent 20 and into the corresponding optical output fiber 22 fortransmission therethrough.

At this point it should be noted that the plurality of optical inputfibers 12 could be replaced in the multiplexing device 10 by acorresponding plurality of laser diodes 28 secured within a couplingdevice 30, such as shown in FIG. 2a (although FIG. 2a shows only asingle 1×4 array). The coupling device 30 serves to precisely group theplurality of laser diodes 28 into a one-dimensional input array. Theplurality of laser diodes 28 are used in place of the plurality ofoptical input fibers 12 to transmit the plurality of monochromaticoptical input beams 24 to the multiplexing device 10. The array of laserdiodes 28, as well as the plurality of optical input fibers 12, mayoperate alone, or may be used with appropriate focusing lenses (notshown) to provide the best coupling and the lowest amount of signal lossand channel crosstalk.

At this point it should be noted that the multiplexing device 10, aswell as all of the multiplexing devices described herein, may beoperated in a converse configuration as a demultiplexing device 40, suchas shown in FIGS. 3a and 3 b. The demultiplexing device 40 is physicallyidentical to the multiplexing device 10, and is therefore numericallyidentified as such. However, the demultiplexing device 40 isfunctionally opposite to the multiplexing device 10. That is, amultiplexed, polychromatic optical input beam 42 is transmitted from theoptical fiber 22, and a plurality of monochromatic optical output beams44 are transmitted to the plurality of optical fibers 12, wherein eachone of the plurality of monochromatic optical output beams 44 istransmitted to a corresponding one of the plurality of optical fibers12. The multiplexed, polychromatic optical input beam 42 issimultaneously carrying a plurality of channels of data, each at aunique wavelength which is preferably, but not required to be, withinthe infrared (IR) region of the electromagnetic spectrum. The pluralityof monochromatic optical output beams 44 are each carrying a singlechannel of data at a corresponding one of the unique wavelengths of themultiplexed, polychromatic optical input beam 42. The multiplexed,polychromatic optical input beam 42 is separated into the plurality ofmonochromatic optical output beams 44 through the combined operation ofthe collimating/focusing lens 16 and the reflective diffraction grating18. Thus, the collimating/focusing lens 16 and the reflectivediffraction grating 18 operate to perform a demultiplexing function.

At this point it should be noted that the plurality of optical fibers 12could be replaced in the demultiplexing device 40 by a correspondingplurality of photodetectors 48 secured within a coupling device 50, suchas shown in FIG. 2b (although FIG. 2b shows only a single 1×13 array).The coupling device 50 serves to precisely group the plurality ofphotodetectors 48 into a one-dimensional input array. The plurality ofphotodetectors 48 are used in place of the plurality of optical fibers12 to receive the plurality of monochromatic optical output beams 44from the demultiplexing device 40. The array of photodetectors 48, aswell as the plurality of optical fibers 12, may operate alone, or may beused with appropriate focusing lenses (not shown) to provide the bestcoupling and the lowest amount of signal loss and channel crosstalk.

At this point it is appropriate to describe in more detail the pluralityof patterned optical input components 14 and the patterned opticaloutput component 20, and the function thereof. Referring to FIG. 4a,there is shown a first embodiment of one of the plurality of patternedoptical input components 14 comprising a collimating microlens 60 and afirst patterned phase mask 62. In the case of the multiplexing device10, the monochromatic optical input beam 24 is transmitted from the core13 of a corresponding optical input fiber 12 to the collimatingmicrolens 60. During this period, the monochromatic optical input beam24 has a generally spherical wavefront 64 and is expanding due togaussian beam diffraction.

The collimating microlens 60 collimates the monochromatic optical inputbeam 24 and then transmits the monochromatic optical input beam 24 tothe first patterned phase mask 62. During this period, the monochromaticoptical input beam 24 is still slightly expanding due to gaussian beamdiffraction, but the monochromatic optical input beam 24 has a generallyplanar wavefront 66 due to the effect of the collimating microlens 60.Also, the collimating microlens 60 causes a widening of thegaussian-shaped passband profile of the multiplexing device 10, asdescribed in more detail below.

The first patterned phase mask 62 introduces a first patterned phasedelay into the monochromatic optical input beam 24 and then transmitsthe monochromatic optical input beam 24 to the collimating/focusing lens16 (not shown). During this period, the monochromatic optical input beam24 is still slightly expanding due to gaussian beam diffraction, but themonochromatic optical input beam 24 also has a first patterned wavefront68 due to the first patterned phase delay that is introduced into themonochromatic optical input beam 24 by the first patterned phase mask62. In accordance with the present invention, the first patternedwavefront 68, and hence the first patterned phase delay, contribute to aflattening of the peak of the gaussian-shaped passband profile of themultiplexing device 10, as described in more detail below.

Referring to FIG. 4b, there is shown a first embodiment of the patternedoptical output component 20 comprising a focusing microlens 70 and asecond patterned phase mask 72. Again in the case of the multiplexingdevice 10, the multiplexed, polychromatic optical output beam 26 istransmitted from the collimating/focusing lens 16 (not shown) to thesecond patterned phase mask 72. During this period, the multiplexed,polychromatic optical output beam 26 is being focused by thecollimating/focusing lens 16 (not shown). Also during this period, themultiplexed, polychromatic optical output beam 26 has a first patternedwavefront 68 due to the first patterned phase delay that is introducedinto the monochromatic optical input beam 24 (as well as all othermonochromatic optical input beams 24 that are combined into themultiplexed, polychromatic optical output beam 26 through the combinedoperation of the collimating/focusing lens 16 and the reflectivediffraction grating 18) by the first patterned phase mask 62.

The second patterned phase mask 72 introduces a second patterned phasedelay into the multiplexed, polychromatic optical output beam 26 andthen transmits the multiplexed, polychromatic optical output beam 26 tothe focusing microlens 70. During this period, the multiplexed,polychromatic optical output beam 26 is still being focused as a resultof the collimating/focusing lens 16 (not shown). Also during thisperiod, the second patterned phase delay that is introduced into themultiplexed, polychromatic optical output beam 26 by the secondpatterned phase mask 72 is added to the first patterned phase delay thatis introduced into the monochromatic optical input beam 24 (as well asall other monochromatic optical input beams 24 that are combined intothe multiplexed, polychromatic optical output beam 26 through thecombined operation of the collimating/focusing lens 16 and thereflective diffraction grating 18) by the first patterned phase mask 62.The addition of the second patterned phase delay to the first patternedphase delay is wavelength dependent. That is, the second patterned phasemask 72 and the first patterned phase mask 62 are designed such that theaddition of the second patterned phase delay to the first patternedphase delay results in either constructive or destructive interferencein the multiplexed, polychromatic optical output beam 26 depending uponthe actual wavelength of each communication channel signal in relationto the expected unique center wavelength of that communication channel.Thus, during this period, the wavefront of the multiplexed,polychromatic optical output beam 26 may vary from a second patternedwavefront 78 as a result of the second patterned phase delay and thefirst patterned phase delay constructively adding to each other whenthey are completely in phase, to a generally planar wavefront 76 as aresult of the second patterned phase delay and the first patterned phasedelay destructively canceling each other when they are 180 degrees outof phase. The constructive adding, or interference, results in morediffracted energy (and thus a greater reduction in the amount of totalenergy at selected locations in the passband profile), while thedestructive canceling, or interference, results in less diffractedenergy (and thus a lesser reduction in the amount of total energy atselected locations in the passband profile). The actual wavelength ofeach communication channel signal may drift off the expected uniquecenter wavelength of that communication channel for a number of reasons,including, for example, temperature and laser diode modulation. In thisparticular embodiment, the second patterned phase mask 72 and the firstpatterned phase mask 62 are designed so as to result in a flattening ofthe peak of the gaussian-shaped passband profile of the multiplexingdevice 10, as described in more detail below.

The focusing microlens 70 focuses the multiplexed, polychromatic opticaloutput beam 26 and then transmits the multiplexed, polychromatic opticaloutput beam 26 toward the optical output fiber 22. During this period,the multiplexed, polychromatic optical output beam 26 varies between agenerally spherical wavefront 77 and a converging patterned wavefront 79due to the effect of the focusing microlens 70 on the multiplexed,polychromatic optical output beam 26. Also during this period, certainportions of the multiplexed, polychromatic optical output beam 26 areslightly more focused on the core 23 of the optical output fiber 22 as aresult of the focusing microlens 70 and due to the above-describeddestructive interference (or lack of the above-described constructiveinterference) on certain portions of the multiplexed, polychromaticoptical output beam 26, while certain other portions of the multiplexed,polychromatic optical output beam 26 are scattered due to theabove-described constructive interference. Thus, those portions of themultiplexed, polychromatic optical output beam 26 that are not scattereddue to the above-described constructive interference are more likely tobe coupled into the core 23 of the optical output fiber 22 fortransmission therethrough.

At this point it should be noted that the focusing microlens 70 causes afurther widening of the gaussian-shaped passband profile of themultiplexing device 10. That is, the combination of the effect of thecollimating microlens 60 on the monochromatic optical input beam 24 (aswell as all other monochromatic optical input beams 24 that are combinedinto the multiplexed, polychromatic optical output beam 26 through thecombined operation of the collimating/focusing lens 16 and thereflective diffraction grating 18), and the effect of the focusingmicrolens 70 on the multiplexed, polychromatic optical output beam 26causes an overall widening of the gaussian-shaped passband profile ofthe multiplexing device 10.

At this point it should be noted that the first patterned phase mask 62may be integrated into the collimating microlens 60, and the secondpatterned phase mask 72 may be integrated into the focusing microlens70. For example, referring to FIG. 5a, there is shown a bi-convexcollimating/focusing microlens 80 having a pure convex surface 82 on oneside and a patterned phase mask convex surface 84 on the opposite side.Alternatively, referring to FIG. 5b, there is shown a plano-convexcollimating/focusing microlens 90 having a pure planar surface 92 on oneside and a patterned phase mask convex surface 94 on the opposite side.

At this point it should be noted that other types of microlenses may beused in accordance with the present invention. For example, microlenseshaving concave or diffractive optic imaging surfaces may be used inaccordance with the present invention, and patterned phase masks may beformed on any of these imaging surfaces.

At this point it is appropriate to describe in more detail the manner inwhich the first patterned phase mask 62 and the second patterned phasemask 72 operate to achieve a flattening of the peak of thegaussian-shaped passband profile of the multiplexing device 10. First,it is preferred that the microlenses 60 and 70 (and/or the combinedmicrolens/phase mask) be placed at the focus of the collimating/focusinglens 16 so that the phase mask is imaged back onto its own plane. Hence,if the monochromatic optical input beams 24 or the multiplexed,polychromatic optical output beam 26 are not truncated or aberrated bythe optical system, the phase of the initial wavefront is preserved asFresnel diffraction terms vanish.

Second, since the collimating/focusing lens 16 is preferably oftelecentric design, the wavefront of the monochromatic optical inputbeams 24 or the multiplexed, polychromatic optical output beam 26returning from the optical system only translates across the receivingmicrolens aperture as the illumination wavelength varies over thepassband range (i.e., there is no tilt). Hence, the overlap integral ofthe source and receiver amplitude distributions can be reduced to anintegral over spatial dimensions, without needing an integration overangle.

Third, the mathematical operation of the input microlens apertureamplitude distribution translating over the receiving microlens apertureamplitude distribution is a cross-correlation. With no phase mask, theamplitude distribution is given by the gaussian mode field diametermultiplied by the truncation due to the micro-lens physical aperture.Thus, let,${{G\left( {x,y} \right)} \equiv {{gaussian}\quad {amplitude}\quad {distribution}}} = ^{- {\lbrack{{(\frac{x}{a})}^{2} + {(\frac{y}{a})}^{2}}\rbrack}}$

wherein a is equal to 1/e (amplitude mode field radius), and let,

R(x,y)≡Rectangular Aperture Function={1:x,y≦L,O otherwise}

wherein L is equal to ½ (aperture width).

The amplitude distribution at the microlens with no phase mask is,

Ap _(o)(x,y)=G(x,y)R(x,y)

The amplitude distribution at the microlens with a phase mask is,

 AP _(m)(x,y)=G(x,y)R(x,y)P(x)=Ap _(o)(x,y)P(x)

wherein P(x) never is greater than 1 or less than −1. Hence, theamplitude and therefore coupled energy into the fiber is never greaterthan the non-phase masked case for the same gaussian profile andaperture.

Let the phase mask function be a coarse sinusoidal (or cosinusoidal)transmission grating in the x direction:${P(x)} = ^{{- i} \cdot \varphi \cdot {\sin {({2.5\pi \frac{x}{L}})}}}$

wherein φ is the amplitude of the phase profile (i e., 0.1π), and L isthe half-width of the aperture.

The sinusoidal phase function can be expanded into a Jacobi series inorder to determine the amplitude of each diffracted order from thecoarse phase grating mask. The amplitude for the nth diffracted order isgiven by an n^(th) order Bessel function coefficient. The energy coupledinto the receiving fiber is given by the 0^(th) order.

e ^(i·φ·sin(θ)) =J ₀(φ)+2J ₂(φ)cos(2θ)+2J ₄(φ)cos(4θ)+ . . . +2i[J₁(φ)sin(θ)+J ₃(φ)sin(3θ)+ . . . ]

wherein J₀ is a Bessel function of order n. For φ=0.1π, J₀=0.975,J₁=0.155, J₂=0.012, J₃=0.00064, . . .

The resultant amplitude distribution after the receiver phase mask, asthe wavelength is varied over the passband, can be calculated bymultiplying the source and receiver amplitude profiles together with alateral shift of the source on the receiver corresponding to thelocation within the passband. A one-dimensional cross-correlation ofAp*(x,y)_(source) with Ap(x,y)_(receiver) computes the fiber couplingamplitude overlap integral as a function of location in the passband(square result to get energy): $\begin{matrix}{{A(u)} = {\int_{- L}^{L}{\int_{{- L}/2}^{L/2}{{{Ap}_{S}\left( {x,y} \right)}{{Ap}_{R}\left( {{x + u},y} \right)}{y}{x}}}}} \\{= {{{Ap}_{S}^{*}\left( {x,y} \right)} \otimes {{Ap}_{R}\left( {x,y} \right)}}}\end{matrix}$

Letting the source and receiver phase masks be equal, and retaining onlythe first order diffraction terms from the series expansion, theresultant amplitude of the source multiplied by the receiver, as thesource is shifted by Δx is: $\begin{matrix}{{A\left( {x,y,{\Delta \quad x}} \right)} = \quad {{{Ap}_{o}\left( {x,y} \right)}{{{Ap}_{o}\left( {{x + {\Delta \quad x}},y} \right)} \cdot}}} \\{\quad \left\lbrack {{J_{0}^{2}(\varphi)} + {2{i \cdot {J_{1}(\varphi)}}{J_{0}(\varphi)}\left\lbrack {{\sin \left( {2{\pi \left( \frac{2.5}{L} \right)}x} \right)} +} \right.}} \right.} \\{\left. \quad {\sin \left( {2{\pi \left( \frac{2.5}{L} \right)}\left( {x + {\Delta \quad x}} \right)} \right)} \right\rbrack +} \\{\quad {2{{J_{1}^{2}(\varphi)}\left\lbrack {{\cos \left( {2{\pi \left( \frac{2.5}{L} \right)}\left( {{2x} + {\Delta x}} \right)} \right)} -} \right.}}} \\{\quad {2{{J_{1}^{2}(\varphi)}\left\lbrack {{\cos \left( {2{\pi \left( \frac{2.5}{L} \right)}\left( {{2x} + {\Delta x}} \right)} \right)} -} \right.}}} \\\left. \left. \quad {\cos \left( {2{\pi \left( \frac{2.5}{L} \right)}\left( {{- \Delta}\quad x} \right)} \right)} \right\rbrack \right\rbrack\end{matrix}$

Integrating the above over x and y as a function of Δx, and squaring togive intensity, gives the passband for the sinusoidal phase mask.

By increasing the spatial frequency at the edge of the aperture andincreasing the amplitude of the phase modulation with respect to thecenter, steeper slopes in the rejection region can also be obtained.Also, orienting the phase grating at an angle with respect to the fiberarray direction will cause the unwanted diffraction orders to fallout-of-line to the fiber array, potentially improving cross-talkrejection. It should be noted, however, that the spatial frequencycomponent in the v-groove direction needs to be equal to the nominalcase. Further, placing phase masked microlenses directly adjacent tonon-phase masked microlenses can ease manufacturing alignment and reducepart count logistics. For example, referring to FIG. 6, there is shown asubstrate 100 having an array of microlenses formed therein. The arrayof microlenses is arranged into a first column 102 and a second column104. The microlenses in the first column 102 have patterned phase masksformed therein/on, while the microlenses in the second column 104 do nothave patterned phase mask formed therein/on. Thus, the substrate 100 canbe shifted such that the microlenses in either the first column 102 orthe second column 104 are aligned with the plurality of optical inputfibers 12, as well as the corresponding plurality of patterned opticalinput components 14, which are arranged into one-dimensional inputarrays (e.g., 1×33 arrays).

At this point it is appropriate to describe a specific working exampleof the demultiplexing device 40 as described above in FIG. 3 thatincorporates the present invention passband profile reshaping conceptsjust described. Assume that the demultiplexing device 40 proposes 100Ghz channel spacing, which results in approximately 0.8 nanometersseparation between communication channels near a 1550 nanometer centerwavelength. The combination of the collimating/focusing lens 16 and thereflective diffraction grating 18 creates a 55 micron focus spot spacingbetween the communication channels at the focal plane of thecollimating/focusing lens 16. Standard optical fibers (SMF-28) have agaussian 1/e-squared mode field diameter (MFD) of 10.6 microns at theend of optical fiber 22. The optical system of the multiplexing device10 creates a 55 micron shift of focus spot with a 0.8 nanometer changeof incident wavelength. As a result of the small ratio of 10.6 micronMFD out of 55 micron spacing, there are large gaps in coupling betweencommunication channels and the region over which coupling is high isquite narrow. As described above, the shape of the coupling with respectto wavelength is called the passband.

Using non-phase masked microlenses (i.e., using no patterned phase maskseither separate from or integrated with the microlenses) in front ofboth the optical fibers 12 and the optical fiber 22, the diameter ofeach of the plurality of monochromatic optical output beams 44 can beoptically re-formed to a larger size. For example, the full angledivergence in radians of a gaussian beam is given by:$\theta = {\frac{4}{\pi} \cdot \frac{\lambda}{d}}$

wherein λ is equal to wavelength and d is equal to MFD_(faber). For amicrolens focal length of 200 microns, a larger apparent mode fielddiameter of 37 microns can be produced as follows:${MFD} = {{\theta \cdot f} = {{\frac{4}{\pi} \cdot \frac{1.55}{10.6} \cdot 200} = 37}}$

The gaussian-shaped passband profile that is widened as a result of theabove-described use of non-phase masked microlenses is shown in FIG. 7.The widened gaussian-shaped passband profile shown in FIG. 7 has thecharacteristics of:

Passband (1 dB down): 0.25 nm, 31 GHz

Adjacent Channel Isolation at 1 dB down point: −36.5 dB

In accordance with the present invention, a patterned phase mask isformed on/in (or added in series with) the microlenses so as to flattenthe peak of the gaussian-shaped passband profile of the demultiplexingdevice 40. For example, a periodic patterned phase mask may be formedon/in (or added in series with) the microlenses so as to flatten thepeak of the gaussian-shaped passband profile of the demultiplexingdevice 40. More specifically, a cosinusoidal patterned phase mask havinga period of 22 microns and amplitude of 0.1 n is formed on/in (or addedin series with) the microlenses. The profile of the cosinusoidalpatterned phase mask is given by the following equation:${{Phase}\quad (x)} = ^{{i \cdot 0.1}\pi \quad {\cos {({\frac{x}{22}2\pi})}}}$

and is shown in FIG. 8, wherein arg is equal to:$0.1\quad {\pi \cdot {\cos \left( {{\frac{x}{22} \cdot 2}\pi} \right)}}$

The passband profile that is flattened as a result of theabove-described use of cosinusoidal patterned phase mask microlenses isshown in FIG. 9. The widened and flattened passband profile shown inFIG. 9 has the characteristics of:

Passband (1 dB down): 0.338 nm, 42 GHz

Adjacent Channel Isolation at 1 dB down point: −29.7 dB

Referring to FIG. 10a, the periodic wavefront profiles that are formedfrom the cosinusoidal patterned phase mask microlenses are shownconstructively adding to each other when they are completely in phase oncenter channel, thereby diffracting the maximum amount of energy out ofthe receiving fiber core. Referring to FIG. 10b, the periodic wavefrontprofiles are shown destructively canceling each other when they are 180degrees out of phase off center channel. In this scenario, the image ofthe input phase pattern impinges out of phase on the output phasepattern. When the amount of off-center wavelength shift corresponds to a180 degree shift of the phase pattern profile, the patterns cancel,thereby coupling all of the light into the receiving fiber core.

Referring to FIG. 11, a plot of the widened gaussian-shaped passbandprofile 106 as shown in FIG. 7 is shown in comparison to the widened andflattened passband profile 108 as shown in FIG. 9. As can be seen fromthis comparison, the addition of the cosinusoidal patterned phase masksto the microlenses also causes a steepening of the sideband slopes dueto energy loss in certain diffraction orders. The points where the twoplots intersect (identified by the X's in FIG. 11) are where theperiodic wavefront profiles destructively cancel each other when theyare 180 degrees out of phase off center channel.

In accordance with the other aspects of the present invention, anon-periodic patterned phase mask may alternatively be formed on/in (oradded in series with) the microlenses so as to flatten the peak of thegaussian-shaped passband profile of the demultiplexing device 40. Morespecifically, a chirped patterned phase mask having increasing amplitudeand spatial frequency at the periphery may alternatively be formed on/in(or added in series with) the microlenses. The profile of the chirpedpatterned phase mask is given by the following equation:${{Phase}\quad (x)} = ^{{i \cdot 0.1}{{\pi {\lbrack{1 + {({{160x}})}^{3}}\rbrack}} \cdot {\lbrack{{{\sin\lbrack\frac{x \cdot {({1 + {{12,000x^{3}}}})}}{27.5}\rbrack} \cdot 2}\pi}\rbrack}}}$

and is shown in FIG. 12, wherein arg is equal to:$0.1{{\pi \left\lbrack {1 + \left( {{160x}} \right)^{3}} \right\rbrack} \cdot \left\lbrack {{{\sin\left\lbrack \frac{x \cdot \left( {1 + {{12,000x^{3}}}} \right)}{27.5} \right\rbrack} \cdot 2}\pi} \right\rbrack}$

The passband profile that is flattened as a result of theabove-described use of chirped patterned phase mask microlenses is shownin FIG. 13. The widened and flattened passband profile shown in FIG. 13has the characteristics of:

Passband (1 dB down): 0.316 nm, 39.5 GHz

Adjacent Channel Isolation at 1 dB down point: −35.8 dB

In view of the foregoing, it follows that there are many variations ofperiodic (e.g., sinusoidal, cosinusoidal, triangular, square, etc.),modulated periodic (e.g., combinations of periodic functions having morethan one frequency), and nonperiodic (e.g., chirped, random, etc.)patterns that can be formed on/in (or added in series with) themicrolenses in accordance with the present invention. Also, the depthand width of the patterned phase masks can be varied to control theamount of diffracted energy in accordance with the present invention.Further, the patterned phase masks may be designed in accordance withthe present invention so as to result in the reshaping of the passbandprofiles of multiplexing devices in other ways than the flattening ofthe peak of a gaussian-shaped passband profile or the steepening of thesideband slopes of a gaussian-shaped passband profile.

At this point it should be noted that it is within the scope of thepresent invention to provide wavelength divisionmultiplexing/demultiplexing devices in accordance with the presentinvention using any or all of the concepts and/or features described inU.S. Pat. No. 5,999,672, issued Dec. 7, 1999; U.S. Pat. No. 6,011,884,issued Jan. 4, 2000; U.S. patent application Ser. No. 09/257,045 filedFeb. 25, 1999; U.S. patent application Ser. No. 09/323,094, filed Jun.1, 1999; U.S. patent application Ser. No. 09/342,142, filed Jun. 29,1999; U.S. patent application Ser. No. 09/382,492, filed Aug. 25, 1999;U.S. patent application Ser. No. 09/382,624, filed Aug. 25, 1999; U.S.patent application Ser. No. 09/363,041, filed Jul. 29, 1999; U.S. patentapplication Ser. No. 09/363,042, filed Jul. 29, 1999; U.S. patentapplication Ser. No. 09/392,670, filed Sep. 8, 1999; and U.S. patentapplication Ser. No. 09/392,831, filed Sep. 8, 1999; all of which arehereby incorporated herein by reference. For example, an wavelengthdivision multiplexing/demultiplexing device in accordance with thepresent invention may be wholly or partially integrated, and differenttypes of lenses and lens configurations may be used.

In summary, the present invention comprises patterned phase masks thatare formed in/on or added in series with microlenses that are attachedor disposed adjacent to the ends of optical fibers in wavelengthdivision multiplexing/demultiplexing devices. In any case, the patternedphase masks are preferably placed at the focus of the maincollimating/focusing lens of the wavelength divisionmultiplexing/demultiplexing device.

The microlenses are used to widen a gaussian-shaped passband profile.The patterned phase masks cause energy to be diffracted in certainlocations within the passband profile, thereby selectively reducing theamount of energy that is coupled into the core of the receiving opticalfiber. That is, at certain locations within the passband profile, thepatterned phase masks cause either constructive or destructiveinterference to occur as incident wavelength varies over the passbandprofile. The constructive interference results in more diffracted energy(and thus a greater reduction in the amount of total energy at selectedlocations in the passband profile), while the destructive interferenceresults in less diffracted energy (and thus a lesser reduction in theamount of total energy at selected locations in the passband profile).Also, the depth and width of the patterned phase masks can be varied tocontrol the amount of diffracted energy.

In the specific exemplary embodiment described herein, constructiveinterference is used to reduce the transmitted energy efficiency at thecenter and edges of the passband profile, thereby flattening the peak ofa gaussian-shaped passband profile and steepening the sideband slopes ofa gaussian-shaped passband profile. That is, energy is discarded at thecenter and edges of the gaussian-shaped passband profile with respect tothe shoulders of the desired passband shape. The amount of energy thatis discarded at the center of the passband profile is tailored to matchthe inverse of the peak of the gaussian-shaped passband profile. Despitethe particular application and results described above, the overalladvantage of the present invention is the ability to vary the amount ofthe effect over the width of the passband profile.

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of thepresent invention, in addition to those described herein, will beapparent to those of ordinary skill in the art from the foregoingdescription and accompanying drawings. Thus, such modifications areintended to fall within the scope of the following appended claims.Further, although the present invention has been described herein in thecontext of a particular implementation in a particular environment for aparticular purpose, those of ordinary skill in the art will recognizethat its usefulness is not limited thereto and that the presentinvention can be beneficially implemented in any number of environmentsfor any number of purposes. Accordingly, the claims set forth belowshould be construed in view of the full breath and spirit of the presentinvention as disclosed herein.

What is claimed is:
 1. An improved wavelength division multiplexingdevice having a diffraction grating for combining a plurality ofmonochromatic optical beams into a multiplexed, polychromatic opticalbeam, the improvement comprising: a plurality of patterned optical inputcomponents corresponding to the plurality of monochromatic opticalbeams, each of the plurality of patterned optical input components forintroducing a first patterned phase delay into a corresponding one ofthe plurality of monochromatic optical beams; and a patterned opticaloutput component for introducing a second patterned phase delay into themultiplexed, polychromatic optical beam; wherein the first patternedphase delay and the second patterned phase delay are added so as toreshape the passband of the improved wavelength division multiplexingdevice.
 2. The improved wavelength division multiplexing device asdefined in claim 1, wherein the plurality of patterned optical inputcomponents comprises: a plurality of patterned phase masks, each of theplurality of patterned phase masks for introducing the first patternedphase delay into a corresponding one of the plurality of monochromaticoptical beams.
 3. The improved wavelength division multiplexing deviceas defined in claim 2, wherein each of the plurality of patterned phasemasks is formed on a corresponding collimating microlens.
 4. Theimproved wavelength division multiplexing device as defined in claim 3,wherein each corresponding collimating microlens contributes to awidening of the passband of the improved wavelength divisionmultiplexing device.
 5. The improved wavelength division multiplexingdevice as defined in claim 2, wherein each of the plurality of patternedphase masks is formed in a corresponding collimating microlens.
 6. Theimproved wavelength division multiplexing device as defined in claim 5,wherein each corresponding collimating microlens contributes to awidening of the passband of the improved wavelength divisionmultiplexing device.
 7. The improved wavelength division multiplexingdevice as defined in claim 2, wherein the plurality of patterned opticalinput components further comprises: a plurality of collimatingmicrolenses, each of the plurality of collimating microlenses forcollimating a corresponding one of the plurality of monochromaticoptical beams.
 8. The improved wavelength division multiplexing deviceas defined in claim 7, wherein each of the plurality of collimatingmicrolenses contributes to a widening of the passband of the improvedwavelength division multiplexing device.
 9. The improved wavelengthdivision multiplexing device as defined in claim 2, wherein each of theplurality of patterned phase masks has a periodic phase profile.
 10. Theimproved wavelength division multiplexing device as defined in claim 9,wherein the passband of the improved wavelength division multiplexingdevice is a gaussian-shaped passband having a peak, wherein the periodicphase profile of each patterned phase mask contributes to a flatteningof the peak of the gaussian-shaped passband of the improved wavelengthdivision multiplexing device.
 11. The improved wavelength divisionmultiplexing device as defined in claim 9, wherein the passband of theimproved wavelength division multiplexing device is a gaussian-shapedpassband having sideband slopes, wherein the periodic phase profile ofeach patterned phase mask contributes to a steepening of the sidebandslopes of the gaussian-shaped passband of the improved wavelengthdivision multiplexing device.
 12. The improved wavelength divisionmultiplexing device as defined in claim 2, wherein each of the pluralityof patterned phase masks has a non-periodic phase profile.
 13. Theimproved wavelength division multiplexing device as defined in claim 12,wherein the passband of the improved wavelength division multiplexingdevice is a gaussian-shaped passband having a peak, wherein thenon-periodic phase profile of each patterned phase mask contributes to aflattening of the peak of the gaussian-shaped passband of the improvedwavelength division multiplexing device.
 14. The improved wavelengthdivision multiplexing device as defined in claim 12, wherein thepassband of the improved wavelength division multiplexing device is agaussian-shaped passband having sideband slopes, wherein thenon-periodic phase profile of each patterned phase mask contributes to asteepening of the sideband slopes of the gaussian-shaped passband of theimproved wavelength division multiplexing device.
 15. The improvedwavelength division multiplexing device as defined in claim 2, whereineach of the plurality of patterned phase masks has a modulated periodicphase profile.
 16. The improved wavelength division multiplexing deviceas defined in claim 1, wherein the patterned optical output componentcomprises: a patterned phase mask for introducing the second patternedphase delay into the multiplexed, polychromatic optical beam.
 17. Theimproved wavelength division multiplexing device as defined in claim 16,wherein the patterned phase mask is formed on a focusing microlens. 18.The improved wavelength division multiplexing device as defined in claim17, wherein the focusing microlens contributes to a widening of thepassband of the improved wavelength division multiplexing device. 19.The improved wavelength division multiplexing device as defined in claim16, wherein the patterned phase mask is formed in a focusing microlens.20. The improved wavelength division multiplexing device as defined inclaim 19, wherein the focusing microlens contributes to a widening ofthe passband of the improved wavelength division multiplexing device.21. The improved wavelength division multiplexing device as defined inclaim 16, wherein the patterned optical output component furthercomprises: a focusing microlens for focusing the multiplexed,polychromatic optical beam.
 22. The improved wavelength divisionmultiplexing device as defined in claim 21, wherein the focusingmicrolens contributes to a widening of the passband of the improvedwavelength division multiplexing device.
 23. The improved wavelengthdivision multiplexing device as defined in claim 16, wherein thepatterned phase mask has a periodic phase profile.
 24. The improvedwavelength division multiplexing device as defined in claim 23, whereinthe passband of the improved wavelength division multiplexing device isa gaussian-shaped passband having a peak, wherein the periodic phaseprofile of the patterned phase mask contributes to a flattening of thepeak of the gaussian-shaped passband of the improved wavelength divisionmultiplexing device.
 25. The improved wavelength division multiplexingdevice as defined in claim 23, wherein the passband of the improvedwavelength division multiplexing device is a gaussian-shaped passbandhaving sideband slopes, wherein the periodic phase profile of thepatterned phase mask contributes to a steepening of the sideband slopesof the gaussian-shaped passband of the improved wavelength divisionmultiplexing device.
 26. The improved wavelength division multiplexingdevice as defined in claim 16, wherein the patterned phase mask has anon-periodic phase profile.
 27. The improved wavelength divisionmultiplexing device as defined in claim 26, wherein the passband of theimproved wavelength division multiplexing device is a gaussian-shapedpassband having a peak, wherein the non-periodic phase profile of thepatterned phase mask contributes to a flattening of the peak of thegaussian-shaped passband of the improved wavelength divisionmultiplexing device.
 28. The improved wavelength division multiplexingdevice as defined in claim 26, wherein the passband of the improvedwavelength division multiplexing device is a gaussian-shaped passbandhaving sideband slopes, wherein the non-periodic phase profile of thepatterned phase mask contributes to a steepening of the sideband slopesof the gaussian-shaped passband of the improved wavelength divisionmultiplexing device.
 29. The improved wavelength division multiplexingdevice as defined in claim 16, wherein the patterned phase mask has amodulated periodic phase profile.
 30. The improved wavelength divisionmultiplexing device as defined in claim 1, wherein the plurality ofpatterned optical input components and the patterned optical outputcomponent cause either constructive or destructive interference to occuras wavelength varies over the passband of the improved wavelengthdivision multiplexing device beam when the first patterned phase delayand the second patterned phase delay are added.
 31. The improvedwavelength division multiplexing device as defined in claim 1, whereinthe plurality of monochromatic optical beams and the multiplexed,polychromatic optical beam are arranged in input and output arrays,respectively, wherein each of the plurality of patterned optical inputcomponents and the patterned optical output component has a patternedphase mask, and wherein each patterned phase mask is oriented at anangle relative to the input and output arrays.
 32. The improvedwavelength division multiplexing device as defined in claim 1, whereinat least the plurality of patterned optical input components or thepatterned optical output component are formed adjacent to a plurality ofnon-patterned optical input components or a non-patterned optical outputcomponent, respectively.
 33. An improved wavelength divisiondemultiplexing device having a diffraction grating for separating amultiplexed, polychromatic optical beam into a plurality ofmonochromatic optical beams, the improvement comprising: a patternedoptical input component for introducing a first patterned phase delayinto the multiplexed, polychromatic optical beam; and a plurality ofpatterned optical output components corresponding to the plurality ofmonochromatic optical beams, each of the plurality of patterned opticaloutput components for introducing a second patterned phase delay into acorresponding one of the plurality of monochromatic optical beams;wherein the first patterned phase delay and the second patterned phasedelay are added so as to reshape the passband of the improved wavelengthdivision demultiplexing device.
 34. The improved wavelength divisiondemultiplexing device as defined in claim 33, wherein the patternedoptical input component comprises: a patterned phase mask forintroducing the first patterned phase delay into the multiplexed,polychromatic optical beam.
 35. The improved wavelength divisiondemultiplexing device as defined in claim 34, wherein the patternedphase mask is formed on a collimating microlens.
 36. The improvedwavelength division demultiplexing device as defined in claim 35,wherein the collimating microlens contributes to a widening of thepassband of the improved wavelength division demultiplexing device. 37.The improved wavelength division demultiplexing device as defined inclaim 34, wherein the patterned phase mask is formed in a collimatingmicrolens.
 38. The improved wavelength division demultiplexing device asdefined in claim 37, wherein the collimating microlens contributes to awidening of the passband of the improved wavelength divisiondemultiplexing device.
 39. The improved wavelength divisiondemultiplexing device as defined in claim 34, wherein the patternedoptical output component further comprises: a collimating microlens forcollimating the multiplexed, polychromatic optical beam.
 40. Theimproved wavelength division demultiplexing device as defined in claim39, wherein the collimating microlens contributes to a widening of thepassband of the improved wavelength division demultiplexing device. 41.The improved wavelength division demultiplexing device as defined inclaim 34, wherein the patterned phase mask has a periodic phase profile.42. The improved wavelength division demultiplexing device as defined inclaim 41, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having a peak,wherein the periodic phase profile of the patterned phase maskcontributes to a flattening of the peak of the gaussian-shaped passbandof the improved wavelength division demultiplexing device.
 43. Theimproved wavelength division demultiplexing device as defined in claim41, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having sidebandslopes, wherein the periodic phase profile of the patterned phase maskcontributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.
 44. The improved wavelength divisiondemultiplexing device as defined in claim 34, wherein the patternedphase mask has a non-periodic phase profile.
 45. The improved wavelengthdivision demultiplexing device as defined in claim 44, wherein thepassband of the improved wavelength division demultiplexing device is agaussian-shaped passband having a peak, wherein the non-periodic phaseprofile of the patterned phase mask contributes to a flattening of thepeak of the gaussian-shaped passband of the improved wavelength divisiondemultiplexing device.
 46. The improved wavelength divisiondemultiplexing device as defined in claim 44, wherein the passband ofthe improved wavelength division demultiplexing device is agaussian-shaped passband having sideband slopes, wherein thenon-periodic phase profile of the patterned phase mask contributes to asteepening of the sideband slopes of the gaussian-shaped passband of theimproved wavelength division demultiplexing device.
 47. The improvedwavelength division demultiplexing device as defined in claim 34,wherein the patterned phase mask has a modulated periodic phase profile.48. The improved wavelength division demultiplexing device as defined inclaim 33, wherein the plurality of patterned optical output componentscomprises: a plurality of patterned phase masks, each of the pluralityof patterned phase masks for introducing the second patterned phasedelay into a corresponding one of the plurality of monochromatic opticalbeams.
 49. The improved wavelength division demultiplexing device asdefined in claim 48, wherein each of the plurality of patterned phasemasks is formed on a corresponding focusing microlens.
 50. The improvedwavelength division demultiplexing device as defined in claim 49,wherein each corresponding focusing microlens contributes to a wideningof the passband of the improved wavelength division demultiplexingdevice.
 51. The improved wavelength division demultiplexing device asdefined in claim 48, wherein each of the plurality of patterned phasemasks is formed in a corresponding focusing microlens.
 52. The improvedwavelength division demultiplexing device as defined in claim 51,wherein each corresponding focusing microlens contributes to a wideningof the passband of the improved wavelength division demultiplexingdevice.
 53. The improved wavelength division demultiplexing device asdefined in claim 48, wherein the plurality of patterned optical outputcomponents further comprises: a plurality of focusing microlenses, eachof the plurality of focusing microlenses for focusing a correspondingone of the plurality of monochromatic optical beams.
 54. The improvedwavelength division demultiplexing device as defined in claim 53,wherein each of the plurality of focusing microlenses contributes to awidening of the passband of the improved wavelength divisiondemultiplexing device.
 55. The improved wavelength divisiondemultiplexing device as defined in claim 48, wherein each of theplurality of patterned phase masks has a periodic phase profile.
 56. Theimproved wavelength division demultiplexing device as defined in claim55, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having a peak,wherein the periodic phase profile of each patterned phase maskcontributes to a flattening of the peak of the gaussian-shaped passbandof the improved wavelength division demultiplexing device.
 57. Theimproved wavelength division demultiplexing device as defined in claim55, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having sidebandslopes, wherein the periodic phase profile of each patterned phase maskcontributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.
 58. The improved wavelength divisiondemultiplexing device as defined in claim 48, wherein each of theplurality of patterned phase masks has a non-periodic phase profile. 59.The improved wavelength division demultiplexing device as defined inclaim 58, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having a peak,wherein the non-periodic phase profile of each patterned phase maskcontributes to a flattening of the peak of the gaussian-shaped passbandof the improved wavelength division demultiplexing device.
 60. Theimproved wavelength division demultiplexing device as defined in claim58, wherein the passband of the improved wavelength divisiondemultiplexing device is a gaussian-shaped passband having sidebandslopes, wherein the non-periodic phase profile of each patterned phasemask contributes to a steepening of the sideband slopes of thegaussian-shaped passband of the improved wavelength divisiondemultiplexing device.
 61. The improved wavelength divisiondemultiplexing device as defined in claim 48, wherein each of theplurality of patterned phase masks has a modulated periodic phaseprofile.
 62. The improved wavelength division demultiplexing device asdefined in claim 33, wherein the patterned optical input component andthe plurality of patterned optical output components cause eitherconstructive or destructive interference to occur as wavelength variesover the passband of the improved wavelength division demultiplexingdevice when the first patterned phase delay and the second patternedphase delay are added.
 63. The improved wavelength divisiondemultiplexing device as defined in claim 33, wherein the multiplexed,polychromatic optical beam and the plurality of monochromatic opticalbeams are arranged in input and output arrays, respectively, whereineach of the patterned optical input component and the plurality ofpatterned optical output components has a patterned phase mask, andwherein each patterned phase mask is oriented at an angle relative tothe input and output arrays.
 64. The improved wavelength divisiondemultiplexing device as defined in claim 33, wherein at least thepatterned optical input component or the plurality of patterned opticaloutput components are formed adjacent to a non-patterned optical inputcomponent or a plurality of non-patterned optical output components,respectively.